DescriptionBritannica Astrolabe - Principle.svg	Schematic drawing for describing the principle of the astrolabe.
Date	published 1911
Source	Encyclopædia Britannica (11th ed.), v. 2, 1911, p. 795.
Author	Unknown authorUnknown author
Permission (Reusing this file)	Public domainPublic domainfalsefalse This image comes from the 13th edition of the Encyclopædia Britannica or earlier. The copyrights for that book have expired in the United States because the book was first published in the US with the publication occurring before January 1, 1929. As such, this image is in the public domain in the United States.
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Caption:

Principle of the Astrolabe. If a solid circle be fixed in any one position and a tube be pivoted on its centre so as to move; and if the line C D be drawn upon the circle pointing towards any object Q in the heavens which lies in the plane of the circle, by turning the tube A B towards any other object P in the plane of the circle, the angle B O D will be the angle subtended by the two objects P and Q at the eye.